It seems that during character creation, my knight can't learn the plate skill (only leather and chain).

I also had no luck finding any store that sells the plate skill. Nothing in Dagger Wound, Ravenshore, or Alvar so far.

Will later tanneries have the plate skill to purchase or is my knight pretty much stuck with only chain mail?

It should be possible in Alvar! Number 8 on this map
It is also possible in Garrote Gorge and Regna

Oh god, finally. Thanks so much.

You are welcome ;) It's hard to imagine a knight without a plate armor, isn't it? ;)

don't go for the knight as the starting char, they're kin of boring :). Take the minotaur or troll :D

I'm enjoying soloing with my knight. I've had great fun with trolls, though. I've also had minotaurs, but never solo.